Assigning custom file descriptors in bash and writing to it

Question

I was playing with bash a bit and was trying to assign a custom descriptor to a file to read from or write to.

Here is what i did:

exec 5> hello.txt    # assigned 5 to hello.txt

echo "hello brother" >& 5        # works

Now the thing that i am not understanding is that if i do this instead

echo "some text" > 5           # does not work, creates a file named '5'

It does not work like the above >&.

I understand:

1. >& redirects stdout & stderr
2. > redirects stdout

What is it that i am missing, is >& necessary when using descriptor?

Answer 1

I understand:

This is exactly the problem - >&5 is ambiguous. That's why you shouldn't use >& and prefer > file 2>&1. See https://wiki.bash-hackers.org/scripting/obsolete

There is a special logic, that if the next token after & is a digit, then it's redirection of stdout to a file descriptor > &5. https://github.com/bminor/bash/blob/ec8113b9861375e4e17b3307372569d429dec814/parse.y#L645